Semiconductor aging reasons why the chip will slow down

Advances in semiconductor technology have been remarkable, with billions of transistors integrated into tiny chips, enabling high-speed, high-efficiency, low-power computing and communications. However, these chips are not eternal, and with time and use, they will experience aging, declining performance, increasing power consumption, diminishing reliability, and even failure.

This is a serious challenge for applications that rely on semiconductor technology,semiconductor testing especially for areas where performance, reliability, and longevity are critical, such as automotive, aerospace, and medical. How does semiconductor aging occur? And what are the physical mechanisms behind it? And what can be done to counteract and mitigate it? In this article, we will reveal the mysteries of semiconductor aging so that you can understand why chips slow down.

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The Root Cause of Semiconductor Aging

Semiconductor aging refers to parameter changes or performance degradation of semiconductor devices caused by various physical, chemical or electrical effects during operation. Usually associated with charges trapped in, for example, insulating layers or metal gaps, it affects the electrical characteristics of the device, such as threshold voltage, current, resistance, etc., which in turn affects the function and performance of the device and the circuit.

Semiconductor aging has a variety of causes, some of which are the result of long-term research,semiconductor failure analysis while others have emerged with technological advances. The following are some of the most common and important semiconductor aging mechanisms:

1. Metal migration

This refers to the movement of metal ions in a metal conductor under the action of an electric current, resulting in gaps or breaks in the metal conductor. This can increase resistance, reduce signal transmission speed, and even cause open-circuit failures. The degree of metal migration is affected by current density and temperature, so it can be mitigated by increasing the metal cross-sectional area or reducing the current.

2. Charge leakage:

Trapped charges in insulators lead to leakage, which may eventually lead to breakdown.aotomatic prober Another mechanism by which electrons pass through a dielectric is tunneling (Fowler-Nordheim tunneling effect), where the tunneling barrier is narrowed by a voltage across the dielectric. The higher the voltage or the thinner the oxide, the easier it is for electrons to tunnel through. As the number of electrons increases, the breakdown voltage of the dielectric decreases, possibly leading to sudden failure.

3. Hot carrier injection

This refers to high energy carriers (electrons or holes) traveling through the gate oxide and being trapped in the gate oxide or at the gate/silicon interface. This changes the charge distribution in the gate oxide, affecting the threshold voltage and drain current of the transistor, and thus the switching speed and power consumption of the transistor.

Hot carrier injection is largely dependent on drain voltage and temperature, and this effect can be mitigated by lowering the drain voltage or using high dielectric constant (High-K) materials.

4. Positive/Negative Bias Temperature Instability

Under negative bias and high temperature conditions, holes in the PMOS transistor drift towards the gate oxide and are trapped, resulting in a drop in threshold voltage. This causes the transistor to switch slower, power consumption increases, and even leakage or short-circuit failures may occur. This phenomenon can be mitigated by lowering the gate voltage or using high dielectric constant materials.

Under positive bias and high temperature conditions, electrons in the NMOS transistor drift toward the gate oxide and are trapped, causing the threshold voltage to rise. This again leads to slower switching of the transistor, increased power consumption, and possibly even leakage or short-circuit failures. Again, this can be mitigated by lowering the gate voltage or using high dielectric constant materials.

5. Temperature cycling fatigue

Temperature cycling fatigue is an important aging mechanism in advanced packaging, stemming from complex multi-chip packages where multiple materials have different coefficients of thermal expansion (CTE). As temperature changes, these materials expand and contract at different rates, resulting in uneven stresses between materials. Over time, these differences can cause metal-to-metal connection failures, leading to discontinuities in the connections. If this long-term temperature cycling is not adequately addressed in the design, devices with mechanical components (e.g., MEMS chips) may experience internal failures. Such failures may result in reduced device accuracy or even complete obsolescence.

6. Other Mechanisms

Other mechanisms, such as oxide breakdown, thermal cycling, and radiation damage, may also affect the lifetime and reliability of semiconductor devices. The degree of influence and probability of occurrence of these mechanisms depend on a variety of factors such as device structure, materials, processes, operating conditions, and application environment.

Strategies for dealing with semiconductor aging

Although semiconductor aging is unavoidable, there are a variety of strategies we can adopt to mitigate and compensate for its effects to ensure the performance and reliability of semiconductor devices and systems.

1. Optimization at the design stage

Select appropriate device structures, materials, processes and parameters, etc. to optimize the performance and reliability of semiconductor devices and systems. Adopting low-power design techniques to reduce power consumption and temperature, using high dielectric constant materials to reduce the electric field strength of the gate oxide layer, and introducing redundant design techniques to improve fault tolerance are all effective means.

2. Evaluation in the verification stage

In the validation phase, the performance changes and failure probability of semiconductor devices and systems during the aging process are evaluated using simulation, testing, and modeling. Predicting the threshold voltage change of transistors with the help of aging simulation tools, using accelerated aging test methods to simulate the aging effect under long-term operating conditions, and using reliability modeling methods to estimate the lifetime of devices and systems all contribute to a better understanding of the effects of aging.